Three bombs have exploded in the north-west Syrian city of Idlib, killing up to 20 people and injuring more than 100 others.

Syrian TV and human rights groups say suicide bombers targeted a military intelligence building and air force intelligence headquarters.

Most of those killed were members of Syria's security forces.

State television said nine people were killed and 100 wounded. It blamed "terrorists" for the attacks, which it said were carried out by "suicide bombers".

It broadcast footage of bloodstains on the ground in one neighbourhood, and groups of angry people denouncing the violence and expressing support for the regime of president Bashar al-Assad.

"Is this the freedom they want?" shouted one man, standing near a woman who was carrying a child with blood running down his forehead.

One building appeared in ruins and cars nearby were flattened by the force of the explosion.

The Syrian Observatory for Human Rights, however, put the death toll closer to 20.

Elsewhere, a car bomb targeting a military vehicle was reported near Damascus, causing an unknown number of casualties.

The explosion targeted a military vehicle, said Abdel Rahman.

"Initial reports indicate there are casualties," he added. "But we cannot yet confirm the number of victims."

An unknown number of civilians living in houses near the site of the explosion were wounded, he said.

The latest violence comes as a United Nations observer team arrives in Syria to monitor the ceasefire that was meant to take force two weeks ago, but is under increasing doubt.

Fingers pointed

On Friday, a suicide car bomb in the heart of the capital killed 11 people.

Anti-regime activists have accused the government of being behind the series of explosions, while the authorities say "terrorists" are responsible.

"We confirm that these tricks no longer fool anyone, especially given the fact that the regime has resorted to these escalations every time there is political movement at the Arab, regional, or international level to find a political solution to the crisis in which the regime kills its people who are demanding freedom," said the activist Local Coordination Committees group.

The Syrian National Council, the main opposition group, said in a statement that the RPG attacks in the capital were "another trick" by the regime to justify its continued crackdown against a revolt that broke out in March last year.

"The Assad regime is trying in various ways to mislead and distract (UN) observers in order to prevent it from carrying out its work," the statement said, also calling for "an international commission of inquiry to uncover who was behind the explosions."

The violence comes despite a UN-backed ceasefire that came into effect on April 12 but has failed to take hold fully.

Veteran peacekeeper Major General Robert Mood urged all sides on Sunday to abide by the ceasefire as he arrived in Damascus to take command of the UN military observer mission overseeing the truce.

The peace plan brokered by UN-Arab League envoy Kofi Annan calls for a commitment to stop all armed violence, a daily two-hour humanitarian ceasefire, media access to all areas affected by the fighting, an inclusive Syrian-led political process, a right to demonstrate and the release of detainees.